Cameras and other image recording devices often use an image sensor, such as a charge-coupled device (CCD) image sensor or a complementary metal-oxide-semiconductor (CMOS) image sensor to capture images. When an image of a scene is captured, the scene can include objects that can be positioned or illuminated in a way that can make it difficult to represent the objects with acceptable detail. For example, an object in the scene can be positioned in a shadow, or the object can be illuminated by a bright light source, such as the sun.
The dynamic range of an image sensor quantifies the ability of the image sensor to adequately image both high light areas in a scene and low dark areas or shadows in the scene. In general, the dynamic range of an image sensor is less than that of the human eye. The limited dynamic range of an image sensor can result in an image losing details in the brighter areas or in the darker areas of the scene.
A variety of algorithms have been produced to improve the dynamic range of image sensors. One such algorithm varies the integration periods (the time light is collected) of the pixels in the image sensor 100, which produces multiple images of a scene. For example, some pixels 102 can have a longer integration period (T1) while other pixels 104 have a shorter integration period (T2) (see FIG. 1). The pixels 104 with the shorter integration period can better capture the brighter areas in a scene and the pixels 102 with the longer integration period can better capture darker areas in the scene. The charge or signals output from the pixels having the shorter and longer integration periods can be combined to produce a final high dynamic range image that has more detail in the lighter and darker areas of the image.
However, when the integration periods of the pixels are varied, the final high dynamic range image can include undesirable motion artifacts. Since the final high dynamic range image is essentially a combination of two images, one image captured with the shorter integration period and another image captured with the longer integration period, objects in the scene can move in between the times the two images are captured. Thus, the scene represented in the image captured with the shorter integration period can differ from the scene represented in the image captured with the longer integration period. This difference can produce motion artifacts, such as blurring, in the combined final high dynamic range image.
Additionally, the signals obtained from the pixels with the shorter integration period can include a higher percentage of noise compared to the signals from the pixels having the longer integration period. The noise can produce undesirable results in the final image and reduce the image quality.